1. Working with an agency does not guarantee that you get a qualified translator. Agencies do not always know which translator is available when confirming your job and you do not always get the same translator for all your jobs.
2. You cannot be absolutely sure that the person editing the project is a professional editor, with native knowledge in both source and target languages, to make sure that the target text sends the same message, with the same style and voice as the source text.
3. By hiring a freelancer you usually get a better price since you take out the middle man.
4. When hiring a freelance translator you can contact him/her directly with questions or new information to increase the quality of the translation, and the translator can discuss all ambiguities and questions directly with you, to achieve the best results possible.
5. When you hire a freelance translator you get first hand information about his/her credentials, publications and expertise.
6. A freelance translator gives you specialization and niche expertise.
7. By using a freelance translator you can make sure that it is only one person doing the translation for urgent translations, and not several translators working on the same project, which can create a mix of styles and skill levels. If a freelance translator cannot fit in the urgent job he/she can usually refer someone from a trusted network of colleagues.
8. Freelance translators are eager to keep you as a direct client and try to provide the best personalized customer service possible.
In short, hiring a freelance translator can be more cost effective and produce better quality translations.
Do you agree with these? Did I forget something?